1. Field of the Invention
The present invention relates generally to a press-fit pin, connector and printed circuit board-connected structure.
2. Description of the Related Art
The back sides of large-scale electronic equipment such as calculators and telephone exchanges have come to be connected to the electronic equipment main unit by a plurality of external cables. As the capabilities of these electronic instruments have increased so, too, has the number of external cables, to the extent that a single back wired board is insufficient and has come to be replaced with a two-piece back wired board assembly.
Specifically, that two-piece back side structure typically consists of a main back wired board electrically connected to the main unit and a sub back wired board fixedly mounted opposite to and a short distance away from the main back wired board. The sub back wired board is electrically connected to the main back wired board, with the external cables connected to the sub back wired board.
The structure that electrically connects the sub back wired board to the main back wired board bears examination. It should be noted at the outset that the density of the required electrical connections makes press-fit pins preferable to wires.
FIGS. 1A, 1B and 1C depict a conventional press-fit pin 1 as well as the state in which it appears when pressed into position in the sub- and main back wired boards. The press-fit pin 1 is suitable for use with a printed circuit board assembly 4 composed of a first printed circuit board 2 and a second printed circuit board 3 disposed opposite each other and separated by a predetermined distance. The press-fit pin 1 has two press-fit sections, an upper first section 1a and a lower second section 1b. When pressed with a force F, the press-fit pin 1 passes through the stages shown in FIGS. 1A and 1B to arrive at the state shown in FIG. 1C, with the first press-fit section 1a inserted in the through-hole 2a of the first printed circuit board 2 and the second press-fit section 1b inserted in the through-hole 3a of the second printed circuit board 3.
That is, the first and second press-fit sections 1a and 1b of the press-fit pin 1 are formed so as to fit the printed circuit board assembly 4, so that, when the press-fit pin 1 has been pressed into place and assumes the state shown in FIG. 1C, the first press-fit section 1a is positioned inside the through-hole 2a of the first printed circuit board 2 and the second press-fit section 1b is positioned inside the through-hole 3a of the second printed circuit board 3. In other words, a distance A between the center 1ac of the first press-fit section 1a and the center 1bc of the second press-fit section 1b is set so as to be equivalent to a distance B between the center of the first printed circuit board 2 in the direction of the thickness of the first printed circuit board 2 and the center of the second printed circuit board 3 in the direction of the thickness of the second printed circuit board 3.
At this point a discussion of the force required to press the press-fit pin 1 into place is necessary. It is useful to think of this required force as two separate forces, one force required to press the first press-fit section 1a into the first through-hole 2a and another force required to press the second press-fit section 1b into the second through-hole 3a. As shown in FIG. 2, the force required to press the first press-fit section la into the first through-hole 2a changes as shown by line I. Similarly, the force required to press the second press-fit section 1b into the second through-hole 3a also changes as shown by line II in FIG. 2. The total force required to press the press-fit pin 1 into place during the course of the pressing process is shown by line III, and is the sum of the force represented by line I and the force represented by line II.
As can be observed from FIG. 2, the insertion of the first press-fit section 1a into the through-hole 2a of the first printed circuit board 2 and the insertion of the second press-fit section 1b into the through-hole 3a of the second printed circuit board 3 takes place at the same time, so the peak 5 of the force represented by line I and the peak 6 of the force represented by line II appear at substantially the same time as well. Accordingly, the total force required to press the press-fit pin 1 into place has a high peak 7 as shown in FIG. 2. As a result, a large compressive force in the axial direction is exerted on the press-fit pin 1 when the press-fit pin 1 is pressed into position and there is thus a possibility that the press-fit pin 1 may be bent in the process. If the press-fit pin 1 is bent the bent press-fit pin 1 must be extracted and replaced with a new press-fit pin 1, interrupting the process of pressing the press-fit pins 1 into place and decreasing the efficiency of the overall production operation.